ATLANTA — Only 28 percent of the 1.2 million Americans living with HIV have the infection under control, increasing the risk that they will spread the disease to others, U.S. health officials said Tuesday.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

A big part of the problem is that one in five U.S. adults infected with HIV do not know it. People can be infected with the AIDS virus for years without developing symptoms. Of those who are aware, only half receive ongoing medical care and treatment, the U.S. Centers for Disease Control and Prevention said in its latest report on HIV in America.

"It's now very clear that we have the tools to stop HIV in an individual and to stop the spread of HIV in a community," CDC Director Dr. Thomas Frieden said in a telephone interview.

"We also know that taking treatment for HIV can prevent people from progressing to AIDS and from developing many of the serious complications of HIV, which unfortunately does remain an incurable infection," Frieden said.

Medications that have been available for 15 years can reduce the amount of virus to low levels. Recent studies have shown that suppressing the virus through treatment reduces the spread of HIV to partners by as much as 96 percent.

CDC's report, released Tuesday ahead of World AIDS day on December 1, focuses on increasing rates of HIV testing and treatment.

It follows new global AIDS priorities set by U.S. Secretary of State Hillary Clinton focused on HIV-fighting drugs as a way of preventing new infections that could bring the goal of "an AIDS-free generation" within reach.

He said the major area of need in the United States is in "strengthening the cascade" of care by improving access and making sure people continue taking their medication to ensure the virus in their body is kept low enough to prevent the spread of the infection.

"The fact that nearly three quarters of Americans living with HIV still have the virus circulating in their bodies, damaging their brains and immune systems and putting their sexual partner at risk is something we think we can do a lot about," he said.

Testing campaign
To reach groups at the greatest risk, the CDC is launching a new campaign urging regular testing for black gay and bisexual men, a population in which both HIV and syphilis infections continue to rise.

Frieden said studies have shown that black gay and bisexual do not engage in riskier behaviors than other gay men.

"It's just that the infection has gotten into this community and therefore it's particularly important that people in the community get tested and treated," he said.

The campaign includes advertising in gay and black neighborhoods in six cities where infections in this population are highest: Atlanta, Baltimore, Houston, New York City, Oakland, California and Washington, D.C.

While the number of Americans newly infected with HIV remained stable between 2006 and 2009, infections rose nearly 50 percent among young black gay and bisexual men, according to a CDC report released in August.